Metallic bellows and method of producing the same



?atented 6, 1931 WILLIAM H. BUELL, OF NEW HAVEN, CONNECTICUT manureBELLQWS AND METHUD OF PRODUCING THE SAME 3% Brewing.

My invention relates to improvements in metallic bellows and the likeand the method of making and producing the same.

These articles have been made for a long time past by various methods,including the spinning as well-as the hydraulic press method shown inUnited States Patent No. 349,718, September 28, 1886, Herman Hollerithand Samuel G. Metcalf, for Apparatus for corrugating metal tubing.

While the articles produced have been practical and useful, still intheir production there has been a large percentage of loss due tobreakage, bursting, etc., which has increased the cost of the articlesand rendered the production of a perfect article a rather uncertainmatter, and those in use frequently break down due to defectiveconstruction or weakened material.

It is with a View to avoiding these objections and producing an articlewhich may be manufactured and formed with a minimum amount of breakageor defectiveness, that 1 made this invention.

1 start with the formation of the tube from which the metallic bellowsare formed. For example, the material of this tube is preferably ofbrass and preferably the brass being approximately 80% copper and 20%zinc.

The important feature of this invention is to have the material of thecompleted tube with the smallest possible uniform grain size and thegreatest tensile strength consistent with requisite ductility. This isaccomplished in the drawing and annealing operations of the tubeprevious to the formation of the tube into the bellows, by annealing ata temperature of approximately 500 to 550 degrees centigrade, forrelatively long periods, such as thirty minutes or so. This results inthe material of the tube having a substantially uniform grain sizewithout mixture of larger grains, which will permit repeated flexingwithout slippage or other malformation of the material structure whichmight result in a permanent set and inefiicient operation.

This process and method of drawing and annealing the tube may be carriedout in such a way as to predict and predetermine Application filedDecember 3, 1927. Serial No. 237,976.

the final essential characteristics of the tube and the bellows, so thatthe above-described advantages will always be obtained, regard. less ofthe composition of the tube.

To describe the previous processes and objections more fully, it isunderstood that in the usual methods of producing thin-wall metallicbellows the spinning operation is usually used, and although the tubebefore the spinning operation might have the desired grain structure,that is, having the grains of uniform size and sufficiently small tosecure the above-mentioned advantages, the s inning operation itself,due to the surface iction and local strains from cold work imposed onthe material and themesultant necessary intermediate annealing at arelatively high temperature, will result in a structural formation ofnon-uniform grain size, with some of the grain structure ex- '7 ceedingmaximum desirable limits. This is due to the fact that the higher theanneal, the larger the resulting grain structure, and due to areas ofunequal cold work, all grains or crystals will not respond equally tolow anneals and will produce a variable struc ture. This is anundesirable property due to the greater liability of structuraldistortion and grain slippage when the completed article is in use.

Heretofore the desirability of starting th forming operation with amaterial having a small uniform grain size has never been recognizedbecause there was not the need for it in spun bellows. By controllingthe drawing operation of the tube or shell and the annealing operationto secure the desirable grain structure and then avoiding anysubstantial alteration of the grain structure in the bellows formingoperation, the resultant bellows is free from local strains due tosubstantial variations in grain size, which tend to shorten and vary thenormal life of the bellows.

I have found that with the use of brass 80% copper and 20% zinc,approximately, and tube thickness of .006, with an anneal of 500 to 550degrees 0., the resultant grain size will be such as to reduce burstingin form ing to a minimum.

As previously stated, by controllin the drawing and the annealing, theresu tant characteristics, as far as grain structure with the attendantadvantages are concerned, may be readily redicted and predetermined, andit is to this road principle that my invention is articularly directed.

n other words, the idea is to keep as close to the transformation ointas possible, consistent with giving su cient ductility to do the work.The transformation point is the point at which crystals which'have beendeformed in cold work are rearranged and take a definite shape and wherethey are in practically a state of rest and not under strain.

Practically all the annealing is done during the drawing and after thetube is formed and before the bellows forming operation. There is noannealing during the forming of the bellows, and while it may benecessary to give a relief anneal, this will be very low, about 250 to300 F. with 80-20 brass.

All of the above temperatures apply to 80-20 brass. However, brass up to-30 might be used or the zinc content may be reduced below 20%. Brass80-20 is the most resistant to corrosion and less liable to season crackthan with higher zinc content. \Vhen the zinc content is below 20%,there is not the life to the material.

Phosphor bronze may be used, as well as nickel copper alloys, and inthese the same type of anneal but at different ranges is used. Thethought is to so anneal the tube that the grain structure is small anduniform so that when the bellows is formed therefrom by bydraulicpressure, the structural distortion and grain slippage will be kept at aminimum. Furthermore, such tubes as might be faulty or weak will beeliminated by bursting during the action of the hydraulic pressure informing, thus insuring a process tested bellows free from pin holes,etc.

In forming the bellows after the tubes are manufactured, I prefer to usethe hydraulic method, which will eliminate the possible changes in grainstructure due to the spinning operation, though it is to be understoodthat other methods may be used than the above, as long as there is nointroduction of cold work from spinning or surface friction, orintermediate or final anneal other than a low temperature relief anneal.The hydraulic method in itself requires greater strength in the tubes towithstand pressure.

The low temperature anneal referred to hereinbefore is not normally usedin drawing as this anneal is so low that the metal is hard :0 drzlrlwand requires more draws for a given If a hydraulic method is used inwhich the bellows is collapsed by the pressure of the hydraulic ram atthe end of the bellows, it has been found essential to allow the ram todwell at the end of its stroke for an apof the tube would be uniformandthat the metal-would respond more uniformly to the low temperatureanneals, because every part of the tube is of necessity worked to thesame degree in being forced through the die. Of course, the use of lowtemperature anneals insures a resultant low percentage of bursts andbreakage in forming.

What I claim is As a new article of manufacture, a thin wall metallicbellows of brass composed of approximately per cent copper and 20 percent zinc, and havlng a uniform grain structure suflicientl small toprevent or minimize slippage and istortion of the structure upon flexingof the bellows within normal working limits.

In testimony that I claim the foregoing, I have hereunto set my handthis 7th day of June, 1927.

WILLIAM H. BUELL.

